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 Plate Tectonic Stories

Cascade du Ray Pic, France

Cascade du Ray Pic

Columnar jointing at Cascade du Ray Pic: © Pete Loader

The iconic basalt columnar jointing seen at Giant’s Causeway can also be seen at a number of locations around the world. One of the most spectacular settings is the Cascade du Ray-Pic waterfalls in the Ardeche, France where the water falls over a stunning outcrop of basaltic columnar jointing, similar to that seen at Giant’s Causeway, though younger in age. 

The Ray-Pic waterfalls are located in the Monts d’Ardèche Regional Nature Park where the water cascades down a 60m thick lava flow that formed around 30-40,000 years ago.  The volcanoes associated with the lava flow are relatively recent and were active between 12,000 and 47,000 years ago. These volcanoes are linked to those in the Bas-Vivarais area of the Massif Central. The basaltic flows from these volcanoes have shaped much of the landscape around Monts d’Ardeche. 

The volcano is at a height of 1293 metres with a vast crater at the peak. The rocks in the area tell us something about the style of eruption that cased the extensive

Cascade du Ray Pic   
 Columnar jointing: © Pete Loader

lava flows. The first part of the eruption was phreatomagmatic meaning that eruptive materials mixed with water and steam to form an explosive eruption.  Over time, the eruption evolved towards a strombolian type eruption and then in its final phase, the crater of the volcano was filled with lava. It was this lava that caused the long basaltic flow which continued for 21km up to Pont-de-Labeaume. The extensive flow of the lava and uniform cooling rate have caused this incredible section of basalt columns to form and the action of water on the rock has exposed the basalt formations for all to see. 

Further reading:

For information on where you can see columnar jointing elsewhere: Wikipedia